1. Field of the Invention
The present invention relates generally to the manufacture of semiconductor devices and, more particularly, to a process for treating the surface of a selected semiconductor substrate having a native oxide layer formed on the surface thereof.
2. Description of the Background Art
In the fabrication of certain semiconductor devices using substrates formed of compound semiconductor materials, such as mercury cadmium telluride, gallium arsenide, indium phosphide, as well as some elemental materials, such as germanium, the presence of native oxide contamination or organic contamination on the substrate surface frequently degrades device performance. In a device in which an insulator layer is deposited on the substrate surface, the presence of the intervening native oxide layer may interfere with optimum electrical performance at the semiconductor/insulator interface. In particular, the device may exhibit degraded current-voltage or capacitance-voltage characteristics, degraded electron transport behavior in the semiconductor material, charge leaks, charge traps, or degraded switching characteristics in the device. Thus, it is advantageous to remove the native oxide layer from the substrate surface prior to the deposition of an insulator layer on this surface.
Known methods for removing native oxide layers and organic surface contamination include both in-situ methods in which the native oxide layer is removed in the same reaction chamber in which the insulator layer is subsequently deposited, and ex-situ methods in which the native oxide layer is removed at a location external to the reaction chamber for insulator layer deposition. Ex-situ methods include treating the substrate surface with various wet acid solutions, such as hydrochloric acid, at elevated temperatures or rinsing with solvents, such as methanol. These ex-situ methods have the major disadvantage that the treated semiconductor surface is vulnerable to contamination in the time period after cleaning and before the insulator layer is deposited. One in-situ method which overcomes the latter problem uses a radio frequency (rf) discharge to generate a plasma of reactive particles, such as atomic hydrogen, that interact with the substrate surface. The latter method is described by F. Capasso and G. F. Williams in the publication entitled "A Proposed Hydrogenation/Nitridization Passivation Mechanism for GaAs and Other III-V Semiconductor Devices, Including InGaAs Long Wavelength Photodetectors", Journal of the Electrochemical Society: Solid State Science and Technology, Vol. 129, No. 4, April 1982, pages 821-824. The disadvantage of using a plasma discharge method for substrate surface preparation is that numerous ionized and neutral particles, as well as high energy radiation are produced and bombard the substrate surface. If the substrate comprises a sensitive device type, such as a device formed of certain compound semiconductor materials (e.g. HgCdTe, InSb, or GaAs), the charged particles and radiation frequently damage these devices. In addition, plasma processing can produce thermal damage to the substrate due to selective absorption of radiation by the substrate and the resultant heating of the substrate. This heating may be sufficient to cause out-diffusion of one or more constituent elements of a compound semiconductor substrate, such as mercury in mercury cadmium telluride.
Thus, the need exists for a low-temperature, charge-free process for minimizing the native oxide layer on the surface of a substrate.